This invention relates to a temperature compensated current source. This current source is shown in an embodiment in which the current varies as a function of the temperature of the system. This current variation as a function of temperature is used to compensate for a load which has changing characteristics as a function of temperature in such a way that the load fluctuations are offset so that the load appears to be temperature independent.
In particular, the present invention is shown as a temperature compensated current source used to provide a source current for a differential amplifier wherein the desired object is to have a constant amplifier gain in view of variations in ambient temperature. One application of this invention is as a head amplifier in a magnetic disk system for computers. Magnetic disk systems must be very stable but have a significant temperature fluctuation from cold-start to warm up.
A further aspect of the present invention is that it was desired to have a temperature compensated current source in which the output current from the current source would increase with temperature at a rate which could be adjusted by changing resistor values. In this way the temperature characteristics of a load, such as, for example, a multiple-stage differential amplifier, could be compensated such that the differential voltage gain of the amplifier would remain constant over a temperature range. The current source must also provide a constant current in view of fluctuations in power supply over a significant range. Also, a desirable characteristic of such a current source would be a high degree of independence from variations because of individual transistor gains. It is known, of course, that where the current source and the load, such as a differential amplifier, are to be temperature compensated, they should be exposed to exactly the same ambient temperature characteristics and this is most easily accomplished by having the entire circuit as part of a monolithic integrated circuit design.